Question

7) In a bicycle race, a biker was riding at 60 km/h alone. She wanted to reduce the drag coefficient by drafting behind her teammate to enjoy a reduced drag, thus saving energy. If she uses the same effort that is the same power (Power = F x V), how fast did she go by drafting? a 68.2 km/h b. 72.4 km/h 79.6 km/h d. 82.5 km/h 0. 8) Cheater knowing Fluid Dynamics? - Red Sox ace Jon Lester pitched against the St. Louis Cardinals in Game 1 of the 2013 World Series, scattering five hits while striking out eight players over 7.2 scoreless innings en route to an 8-1 Boston win for an early 1-0 series lead. But people noticed that he constantly rubbed the ball against the inside of his glove, maybe with resin or some other gel? Or trying to roughen the ball with a tiny piece of sand paper? If this were true, the following was what he had actually achieved in terms of fluid dynamics, EXCEPT: & A ball with gel to make it smooth will create less surface shear stress and thus less drag. b. A roughened ball would make the flow's boundary layer undergo an earlier transition from laminar BL to turbulent BL, so that BL separation was delayed and thus a reduced drag - a faster pitch! c. The drag characteristics of the ball would change drastically with the gel, and so would the ball path - making it harder to hit. d. Vaseline on the ball could make the dirt particles stay while travelling - making it a "rough ball." 9) Froude number Fr = is important in open channel flow of water, because vey a. Open channel flow has a pressure that is different everywhere. b. Open channel flow is with a free surface and the flow is driven by gravity. c. Vgy represented a wave from bottom to surface. d. Wetted perimeter of water channel P can be a rough surface. 10) An open channel flow in a hydraulic lab is designed to line artificially with corrugated metal. To keep the shape and all other conditions the same, the designer can simply replace the corrugated metal with brass and the flow rate (Q, in m/s) of the channel will a. Decrease by 50% b. Increase by 50% c. Double d. Quadruple

Answer 1

As per HOMEWORKLIB POLICY, only one question can be answered. So, the first question is answered as the student has not requested for a particular question.

The drag co-efficient is a function of many factors. The speed of travel, the length of trial in drafting, distance between the cyclists, number of cyclists, direction of wind etc. Howerver, in general it is reported in literature that the drag co-efficient reduces by about 27% due to drafting.

Hence, new drag force = ( 1 - 0.27 ) F = 0.73F

For same power, new velocity = P / F = 60 / 0.73 = 82.2 kmph which is close to option (d).